Methods and apparatus for coating particulate material

ABSTRACT

Methods and apparatus for coating particulate material are provided. The apparatus includes a vessel having a top and a bottom, a vertically extending conduit having an inlet in the vessel and an outlet outside of the vessel, a first fluid inlet in the bottom of the vessel for introducing a transfer fluid, a second fluid inlet in the bottom of the vessel for introducing a coating fluid, and a fluid outlet from the vessel. The method includes steps of agitating a material, contacting the material with a coating material, and drying the coating material to produce a coated material. The invention may be adapted to coat aerogel beads, among other materials. A coated aerogel bead and an aerogel-based insulation material are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from pending U.S. Provisional PatentApplication 60/865,722, filed on Nov. 14, 2006, the disclosure of whichis incorporated by reference herein in its entirety.

The subject matter of the present application may also be related to theinventions described in copending application Ser. No. 11/567,100 filedon Dec. 5, 2006 and copending provisional application 60/868,468, filedon Dec. 4, 2006. The disclosures of these applications are also includedby reference herein in their entirety.

STATE AND FEDERAL FUNDED RESEARCH

The invention described herein was made with New York State supportunder State Grant Number C010331 from the New York State Department ofTransportation. The State of New York may have certain rights to thisinvention.

The invention described herein was also made with support of theNational Aeronautics and Space Administration (NASA) under Federal GrantNumber NNM05AA04A. The U.S. Government may have certain rights to thisinvention.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates, generally, to systems, methods, and apparatusfor coating particulate material and the coated particulate material soproduced. More particularly, the present invention provides improveddraft tube spout fluid bed (DTSFB) having the capability to coatparticles with fluids, for example, for coating aerogel beads to providea useful engineering material, for instance, an improved insulatingmaterial.

2. Description of Related Art

Coating particulate material can often enhance the physical and chemicalproperties of the material, for example, by reducing absorption ofliquids and gases or simply protecting the particulate material fromenvironmental degradation. For instance, the coating of particulatematerial can provide the following enhancements to particulate material:improved insulation properties, both thermal and electrical; improvedabrasion resistance; and improved strength.

Aerogel beads were first developed in the 1930s and are the lightestsolids known. Aerogels are low-density materials that have proven to beeffective insulators. They typically have a thermal conductivity on theorder of 0.01 Watts/meter-Kelvin, that is, less than one-third thethermal conductivity of polyurethane foam. However, only recently hasthe commercial scale production of aerogels been economically feasible.Aerogels are typically referred to by the nicknames “frozen smoke,”“solid smoke,” or “blue smoke.”

Due to their insulating properties and their low density, approximately,140 kilograms per cubic meter, aerogels have been proposed forinsulation in a broad range of applications from insulating liquidnatural gas (LNG) supertankers, to insulating superconductor powercables, to insulating spacecraft, such as, insulating the external fueltanks or crew return vehicle of the space shuttle.

However, typically, untreated aerogels are porous and tend to absorbgases and liquids. For example, about 95% of the surface of aerogelbeads contain pores having an average pore size of about 20 nanometers(nm). The absorption of fluids by aerogels may typically destroy thematerial or, at the very least, interfere with the insulating propertiesof the beads. The present inventors sought to overcome the porous natureof aerogels by coating aerogels to minimize or prevent the absorption orinfiltration of fluids, for example, by applying a polymer coating.However, the very light, low-density nature of aerogels makes themdifficult to handle, especially when attempting to coat these minuteparticles, typically, less than 5 millimeter (mm) in diameter. Aspectsof the present invention overcome these technical difficulties, as wellas overcoming the disadvantages and limitations of the prior art methodsand apparatus.

One device that has been used to handle particulate material is adraft-tube, spout-fluid-bed (DTSFB) mixer. The design and operation ofthe DTSFB mixer were investigated by Littman, et al. and are disclosedin U.S. Pat. Nos. 5,248,222 and 5,254,168, both of Littman (one of theco-inventors of the present invention), et al. (the disclosures of whichare included by reference herein). Recent developments of the DTSFBmixer were reported by Plawsky, et al. (2003), the disclosure of whichis also incorporated by reference herein, in which a “first generation”mixer was disclosed. Further improvements in the DTSFB mixer werereported by Park, et al, (2006) in which a “second generation” DTSFBmixer was designed and tested. (The disclosure of Park, et al. (2006) isalso included by reference herein.) Aspects of the present inventionprovide advantages over both Park, et al, (2006) and Plawsky, et al.(2003), and other prior art methods and apparatus.

SUMMARY OF THE INVENTION

Aspects of the present invention provide improved methods and apparatusfor coating particulate material using different mechanics than theprior art coating systems. From an industrial point of view, aspects ofthe invention are easily scaled up from very small units to very largeunits in a very predictable manner. According to aspects of theinvention, methods and apparatus are provided which produce coatedparticulate materials, for example, coated aerogels, that havingimproved insulation properties, both thermal and electrical; improvedabrasion resistance; and improved strength compared to non-coatedparticulate materials. Aspects of the invention are based on two maincomponents, namely, a pneumatic coating device and a collection device,such as, a vessel containing a bag filter, which is commonly used forair pollution control and solids recovery.

One aspect of the invention is a particulate material coating apparatusincluding a vessel having a top and a bottom, the vessel adapted tocontain the particulate material; a vertically extending conduit (alsoknown as a “draft tube”) having an inlet in the vessel and an outletoutside of the vessel; a first fluid inlet in the bottom of the vessel,the first fluid inlet directed toward the inlet of the verticallyextending conduit wherein a flow of a first fluid introduced by thefirst fluid inlet produces a flow of at least some of the particulatematerial and the first fluid through the vertically extending conduit; asecond fluid inlet in the bottom of the vessel, the second fluid inletadapted to introduce a second fluid to the flow of fluid introduced bythe first fluid inlet, the second fluid adapted to coat at least some ofthe particulate material; and a fluid outlet from the vessel. The secondfluid inlet is typically adapted to introduce the second fluid in theform of a spray, for example, the second fluid inlet may include anorifice, for instance, an orifice having a diameter of about 0.020inches.

In one aspect, the apparatus may include means for regulating the flowof fluid from the fluid outlet from the vessel, for example, anautomated valve, wherein at least one parameter of the flow of theparticulate material and fluid though the vertically extending conduitis varied. The parameter varied may be particle flow velocity, fluidflow velocity, voidage, or a combination thereof, for example, for agiven total fluid inlet flow.

Another aspect of the invention is a method for coating particulatematerial including introducing the particulate material to a vesselhaving a top and a bottom, a vertically extending conduit having aninlet in the vessel and an outlet outside of the vessel, a first fluidinlet in the bottom of the vessel directed toward the inlet of thevertically extending conduit, a second fluid inlet in the bottom of thevessel, and a fluid outlet; introducing a first fluid into the firstfluid inlet to produce a flow of the first fluid that produces a flow ofat least some of the particulate material and the first fluid throughthe vertically extending conduit; introducing a second fluid to thesecond fluid inlet whereby the second fluid is introduced into the flowof the first fluid; and coating at least some of the particulatematerial with the second fluid. In one aspect, the method furthercomprises regulating the flow of fluid from the outlet wherein at leastone parameter of the flow of the particulate material and fluid thoughthe vertically extending conduit is varied. The parameter may includeparticle flow velocity, fluid flow velocity, voidage, or combinationsthereof, for example, for a given total fluid inlet flow. In one aspect,the particulate material comprises aerogel particles and coatingcomprises sealing at least some pores in the aerogel particles. Thesecond fluid may comprise an alcohol, a water-based polymer, asolvent-based polymer, or a polyurethane. The second fluid may be air,nitrogen, an inert gas, or another suitable gas.

Another aspect of the invention is a method for coating aerogel beadsincluding agitating a plurality of aerogel beads with a first fluidstream; contacting the agitated beads with a second fluid stream havingat least one non-volatile component and at least one volatile component;evaporating at least some of the at least one volatile componentcontacting the beads wherein at least some of the non-volatile componentadheres to a surface of the beads. In one aspect, the method may furthercomprise transporting the plurality of aerogel beads and the first fluidthrough a conduit. In another aspect, at least some of the evaporatingis practiced during transport through the conduit.

A further aspect of the invention is a coated aerogel materialcomprising a plurality of aerogel beads at least partially coated with apolymer, for example, coated with a polyvinyl alcohol, a polymethylmethacrylate (PMMA), or a polyurethane, among other volatile materials.In one aspect, the aerogel beads comprise about 1 mm to about 5 mmaerogel beads, typically, about 1 mm to about 3 mm aerogel beads, forexample, about 2 mm aerogel beads. Aspects of the present inventionprovide coated aerogel material having improved insulation properties,both thermal and electrical; improved abrasion resistance; and improvedstrength, among other things, compared to uncoated aerogel materials.

A still further aspect of the invention is an insulating materialcomprising a plurality of aerogel beads at least partially coated with apolymer, for example, coated with a polyvinyl alcohol, a polymethylmethacrylate, or a polyurethane, among other volatile materials. In oneaspect, the aerogel beads comprise about 1 mm to about 5 mm aerogelbeads, typically, about 1 mm to about 3 mm aerogel beads, for example,about 2 mm aerogel beads.

These and other aspects, features, and advantages of this invention willbecome apparent from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention will be readily understood from thefollowing detailed description of aspects of the invention taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram, in cross-section, of a particulatematerial coating apparatus according to one aspect of the invention.

FIG. 2 is a detailed schematic diagram of the lower section of theapparatus shown in FIG. 1 as identified by detail 2 in FIG. 1.

FIG. 3 is a perspective view of a particulate material coating apparatusaccording to another aspect of the invention.

FIG. 4 is a front elevation view of the apparatus shown in FIG. 3.

FIG. 5 is a perspective view of the feeding and treating apparatus shownin FIG. 3.

FIG. 6 is a perspective, in cross section, of the inlet of the feedingand treating apparatus shown in FIG. 5.

FIG. 7 is a photograph of magnified aerogel particles as treatedaccording to aspects of the invention.

FIG. 8 is a photograph of a magnified aerogel particle as treatedaccording to aspects of the invention.

FIG. 9 is a photograph of further magnified aerogel particles as treatedaccording to aspects of the invention.

FIG. 10 is a photograph of further magnified aerogel particles astreated according to aspects of the invention.

DETAILED DESCRIPTION OF ASPECTS OF THE INVENTION

Aspects of the present invention may be utilized to coat particulatematerial in a broad range of applications. For example, aspects of theinvention may be used for, but are not limited to, coating particulates,for example, coating any particulate material that is recognizable bythose of skill in the art, for example, pharmaceuticals; food stuffs;cosmetics; metals, such as, powder manufacturing powder metals;ceramics; and like particulates. Though the following description ofaspects of the invention may refer to the use of aspects of theinvention in coating aerogel beads, aspects of the present invention arenot limited to handling and treating aerogel beads. It will beunderstood that one or more other particulate materials may also behandled and treated according to aspects of the invention in similarfashions.

FIG. 1 is a schematic diagram, in cross-section, of a particulatematerial coating apparatus 10 according to one aspect of the invention.Apparatus 10 includes a vessel 12, for example, a circular cylindricalvessel, though any non-circular or non-cylindrical vessel may be used,as appropriate. Vessel 12 includes a substantially closed top 14 and asubstantially closed bottom 16 and, according to aspects of theinvention, contains particulate material 18. Though closed bottom 16 isillustrated as having a conical, upwardly expanding geometry in FIG. 1,it will be understood that bottom 16 may comprise any conventionalvessel shape, including a circular or rectangular cylindrical bottom 17as shown in phantom in FIG. 1. Particulate material 18 may include anyparticulate material, for example, a powder, pellets, beads, chips,chunks, and the like, which may be metallic or non-metallic, forexample, sand, stone, plastics, polymers, pharmaceuticals, saw dust,wood chips, food particles, ceramics, porous material, catalysts,catalytic materials, absorbents, adsorbents, ion exchange resins, andthe like. In one aspect, particulate material 18 may comprise aerogelbeads, for example, beads of a low-density solid-state material derivedfrom gel in which the liquid component of the gel has been replaced withgas. The aerogel beads may comprise aerogel materials based on silica,alumina, chromia, tin oxide, or carbon, among other materials. Theaerogel beads may have diameters ranging from about 50 micrometers [μm]to about 5 millimeters [mm].

In one aspect, particulate material 18 may comprise a plurality ofparticulate materials, for examples, materials intended to be mixed byapparatus 10, for instance, sand and cement or two or morepharmaceuticals. In one aspect, particulate material 18 may comprise amaterial having sufficient voidage, that is, space between particles,that when placed in vessel 12 a fluid, for example, a gas or liquid, maybe passed through particulate material 18, for example, in a directionindicated by arrows 15. Particulate material 18 may form a level ofmaterial 19, below top 14 of vessel 12 whereby a void space 21 isprovided in top 14 of vessel 12, for example, an annular void space.Void space 21 may provide a plenum into which fluid passes after passingthrough material 18 prior to, for example, exiting vessel 12.

According to aspects of the invention, vessel 12 of apparatus 10includes at least one conduit, pipe, or tube 20 (which may be referredto in the art as a “draft tube”) having an open first end 22 positionedinside vessel 12 and an open second end 24 positioned outside or insideof vessel 12. Conduit 20 may typically be directed vertically withinvessel 12, as shown in FIG. 1; however, conduit 20 may be oriented atany angle, that is, an angle from the vertical, while effecting thedesired function described in this specification and attached claims.Optionally, the open second end 24 of conduit 20 may be located in asecond vessel 25 (shown in phantom in FIG. 1). A typical second vessel25 that may be used in aspects of the invention is described anddiscussed with respect to FIG. 3 below, though any vessel which isadapted to collect particulate material discharged from open second end24 may be used. Conduit 20 may have any convenient cross-section, forexample, circular, oval, or rectangular, but is typically circular incross section. In one aspect, conduit 20 may be directed substantiallyvertically in vessel 12 whereby conduit 20 forms an annular region 26 invessel 12 between the outside of conduit 20 and the inside of vessel 12.

Vessel 12 includes at least one fluid inlet 28 positioned in the bottom16 of vessel 12 for receiving a fluid 36 (that is, a liquid or gas) andat least one fluid outlet 32 positioned in top 14 of vessel 12. Fluid 36may be a multiphase fluid, for example, a fluid containing a liquid andsolids, a fluid containing a liquid and a gas, a fluid containing a gasand solids, or a fluid containing a liquid, a gas, and solids. It willbe understood by those in the art, that the multiphase fluid may containone or more liquids, one or more gases, or one or more different solidsdepending upon the treatment to be performed in vessel 12. Vessel 12 mayalso include at least one inlet 33, for example, positioned in top 14,for instance, for introducing particulate material 18 to vessel 12.Inlet, or fluid jet, 28 comprises a conduit having a fluid outlet 30(see FIG. 2) directed toward inlet 22 of conduit 20. According toaspects of the invention, inlet 28 is so positioned whereby fluidintroduced to inlet 28 and directed toward inlet 22 of conduit 20produces a flow of at least some of particulate material 18 and fluidthrough the conduit 20, as indicated by arrows 23. Due to the typicalexpansion of fluid flow as the fluid leaves inlet 28, the diameter ofinlet 28 may be smaller than the diameter of inlet 22. Also, the spacingof inlet 28 from inlet 22 may be varied, for example, the elevation ofinlet 28 may be varied, for instance, depending upon the nature of thefluid introduced and the particulate material 18. In some aspects of theinvention, the flow of fluid through inlet 28 may be augmented by one ormore additional fluid inlets 29 for introducing a fluid 37, for example,the same or different fluid 36 introduced to inlet 28.

According to aspects of the invention, vessel 12 includes a means ormechanism 40 for introducing a coating fluid 41 to vessel 12. Forexample, as shown in FIG. 1, mechanism 40 may be one or more spraynozzles 43 adapted to introduce fluid 41 to contact and coat at leastsome of the particulate material 18, for example, as material 18 isbeing transported through conduit 20. Spray nozzles 43 may be any fluidinjection device adapted to expose material 18 to fluid 41, for example,spray nozzles 43 may introduce a fine mist of liquid, a flow of liquidin a gas, or a flow of gas. In one aspect, mechanism 40 may comprise oneor more spray nozzles provided by Spraying Systems Company of Wheaton,Ill., for example, a spraying system having an SU2A air atomizing spraynozzle set up with a fluid cap 2050 and air cap 70, having a nozzlediameter of about 0.020 inches, though other spraying nozzle systems maybe used. Coating fluid 41 may comprise any fluid adapted to coatmaterial 18 being handled, and coating fluid 41 may vary depending uponthe nature of material 18 being coated. In one aspect, where material 18comprises aerogel beads, coating fluid 41 may comprise a polyvinylalcohol, for example, an OPADRY water-based cationic polymer provided byColorcon; a polymethyl methacrylate, for example, a water-based anionicpolymer, a solvent based cationic polymer or a solvent-based neutralpolymer marketed under the trademark EUDRAGIT by Degussa; or a urethane,for example, a polyurethane solution or a water-borne polyurethanesolution, among others.

According to aspects of the invention, the outlet 32 may include somemeans 34 for regulating or controlling the flow of fluid through outlet32. Outlet 32 may be a conduit and means 34 may be a valve, for example,a ball, a needle, a globe, or gate valve. In aspects of the invention,means 34 controls the flow of fluid from outlet 32 whereby at least oneparameter of the flow of particulate material 18 and fluid though theconduit 20 is varied. For example, varying the flow through outlet 32may vary particle flow velocity, fluid flow velocity, voidage, or acombination of two or more of these parameters. In one aspect of theinvention, vessel 12 may include at least one means 35 for controllingthe pressure drop across conduit 20. For example, means 35 may comprisea dp cell or a differential pressure indicator having high and lowpressure taps appropriately positioned in vessel 12 and/or vessel 25.Contrary to prior art devices, for example, the device disclosed byPlawsky, et al. (2003), by controlling or regulating the pressure dropacross conduit 20, aspects of the present invention permit the operatorto regulate or control the flow of the particulate material throughconduit 20, for example, to control the flow regime in conduit 20 orcontrol the solids fraction of the particulate material flowing throughconduit 20. In FIG. 1, means 35 is illustrated schematically forreference only; however, in aspects of the invention, a pressure dropacross conduit 20 may be controlled by mean of a restriction in conduit20 or a restriction down stream of conduit 20, for example, arestriction in optional vessel 25 or a restriction in a conduit leadingfrom vessel 25, such as, a valve. The controlling of the pressure dropacross conduit 20 may be practiced by controlling or regulating thepressure in vessel 12, by controlling or regulating the pressure inoptional vessel 25, or both.

FIG. 2 is a detailed schematic diagram of the lower section of theapparatus 10 shown in FIG. 1 as identified by Detail 2 in FIG. 1.According to aspects of the invention, as a fluid, for example, a gas ora liquid, is introduced to vessel 12 through inlet 28, as indicated byarrows 36, the fluid enters vessel 12 and entrains and/or agitates atleast some of particulate material 18 into open end 22 of conduit 20, asindicated by arrows 38, and transfers particulate material 18 throughconduit 20, as indicated by arrow 23. As described in, for example, U.S.Pat. No. 5,248,222, the introduction of a pressurized fluid, typically,air (though other gases or liquids may be used), into inlet 28 (and/orother inlets 29) agitates and/or entrains the particulate material 18above inlet 28 whereby particulate material 18 will flow like a fluid.In one aspect of the invention, this agitation and/or aeration ofparticulate material is often referred to as “fluidization,” whereby anormally solid particulate material 18 is induced to behave somewhatlike a fluid under the influence of the fluid introduced to inlet 28and, possibly, inlets 29. The fluidization of the particulate materialand the consequent creation of a pressure differential between the openend 22 and open end 24 of conduit 20 promotes the flow of the aeratedparticulate material 18 from open end 22, through conduit 20, and out ofopen end 24.

According to aspects of the invention, while material 18 is entrained,agitated, and/or fluidized by fluid introduced by inlet 28, at least onefurther fluid 41 is introduced by means 40, for example, one or morenozzles 43, to contact the material 18 with fluid 41. In one aspect,fluid 41 comprises a fluid adapted to at least coat at least some of thesurface of the individual particles of material 18. In one aspect, atleast 25% of the surface of particulate material 18 is receives at leastsome fluid 41. In another aspect of the invention, at least 50% or evenat least 75%, of the surface area of the material receives at least somefluid 41. In some aspects more than 90% or even substantially 100% ofthe surface area of material 18 may be covered or coated with fluid 41.

During or after coating material 18 with fluid 41, the fluid 41 isallowed to “dry” onto the surface of material 18, for example, byevaporation of any volatile components present in fluid 41, whereby atleast some non-volatile component of fluid 41 adheres to at least someof the surface of particulate material 18, to provide a coatedparticular material 18. In one aspect, at least some of the surface ofparticulate material 18, for example, at least 25% of the surface, iscoated with a non-volatile component of fluid 41. In another aspect ofthe invention, at least 50% or even at least 75%, of the surface area ofthe material is coated with a non-volatile component of fluid 41. Insome aspects, more than 90% or even substantially 100% of the surfacearea of material 18 may be covered or coated with a non-volatilecomponent of fluid 41. According to aspects of the invention, thisdrying or evaporation of volatile components may be accelerated by thefluid flow introduced via inlet 28. For example, the fluid introducedvia inlet 28 may comprise a fluid having little or no concentration ofthe volatile component of fluid 41, for example, fluid 41 may be a lowhumidity air or low humidity nitrogen, among other gases. In anotheraspect, the fluid introduced to inlet 28 may be heated, for example,heated air, to enhance evaporation of the volatile components of fluid41.

In some aspects of the invention, at least some of the fluid introducedthrough inlets 28 and 29 may also pass through particulate material 18in annulus 26, as indicated by arrows 42, and exit vessel 12 throughoutlet 32. Thus, according to aspects of the invention, apparatus 10 maycomprise an apparatus for handling or transporting particulate material18 through conduit 20; an apparatus for treating particulate material 18with a fluid 36, that is, for treating particulate material 18 inconduit 20, in annulus 26, or a combination thereof; an apparatus formixing one or more particulate materials; or a combination thereof.However, unlike prior art apparatus, in apparatus 10 according toaspects of the present invention, the nature of the flow of material inconduit 20 and annulus 26 may be moderated and controlled, for example,by manipulating the pressure drop across conduit 20, for instance, bymanipulating valve 34 in outlet 32. As noted above, the pressure dropacross conduit 20 may be varied in numerous ways according to theinvention, for example, by introducing a restriction to conduit 20; byintroducing a restriction to a down stream flow, for example, by meansof a pressure control element, such as, a valve; or by providing avessel 25 downstream of conduit 20, for example, a vessel in whichpressure is regulated. In one aspect of the invention, the concentrationof the solid particles 18 transferred through conduit 20 may beregulated and/or controlled by regulating and/or controlling thepressure drop across conduit 20, for example, by manipulating a valve inan outlet from a downstream vessel.

Apparatus 10 shown in FIGS. 1 and 2, with or without means 35 forcontrolling the pressure drop across conduit 20, may be used to handle,coat, treat, and/or react particulate material 18 or for handling,treating, or reacting fluid 36. For example, apparatus 10 may comprise amixing apparatus for mixing two or more materials. Apparatus 10 may alsocomprise a treatment apparatus, for example, an apparatus for treatingthe fluid introduced to inlet 28 with the particulate material 18.Apparatus 10 shown in FIGS. 1 and 2, with or without means 35 forcontrolling the pressure drop across conduit 20, may be used to executea chemical or physical reaction, for example, a reaction thatparticulate material 18 may or may not take part in, for example, may ormay not catalyze, using at least part of the fluid streams 36 enteringthrough inlet 28 (or auxiliary inlets 29). A chemical or physicalreaction may take place in the annular region 26, or in conduit 20, orboth in region 26 and in conduit 20. A reaction may also take place indown stream vessel 25. Particulate material 18 may return at least inpart through inlet 33 after residence in vessel 25, for example, where aphysical or chemical reaction may have taken place prior to returnthrough inlet 33, though substantially all of the material 18 passed tovessel 25 may be returned to vessel 12. Typical chemical or physicalreactions that may be practiced in vessel 12 may include, but are notlimited to, catalytic oil cracking, protein separations, particlemixing, and particle coating, among others.

According to aspects of the invention, particulate material 18 maycomprise one or more particulate materials, such as sand and cement,that when aerated, coated, and transported through conduit 20 are atleast partially mixed or agitated to provide a mixture of coatedparticulate material discharged from open end 24 of conduit 20. Forexample, during transport through conduit 20, the inventors surmise thatthe turbulent eddies generated in conduit 20 provide shearing forcesthat overcome particle surface effects, such as van der Waals forces andelectrostatic forces that hold individual particles in clumps, to breakup clusters and clumps of particulate material and provide a moreuniformly mixed material. In another aspect of the invention, asdiscussed above, apparatus 10 may comprise a coating apparatus by whichone or more particulate materials 18 may be coated with a materialcontained in fluid 41 introduced to means 40, for example, a nozzle 43,before or during transport through conduit 20.

FIG. 3 is a perspective view of a particulate material coating apparatus100 according to another aspect of the invention. FIG. 4 is a frontelevation view of apparatus 100 shown in FIG. 3. Apparatus 100 includesa feeding and treating apparatus 102 and a drying and collectingapparatus 104. Similar to apparatus 10 shown in FIGS. 1 and 2, in oneaspect of the invention, feeding and treating apparatus 102 conveysparticulate material while coating the material conveyed, for example,aerogel beads. Apparatus 102 includes a vessel 112, for example, acircular cylindrical vessel, having a substantially closed top 114 and asubstantially closed bottom 116 and, according to aspects of theinvention, contains particulate material 118 (not shown). Particulatematerial 118 may include any particulate material, for example,particulate materials that may comprise particulate material 18described above. In one aspect, particulate material 118 may compriseaerogel beads. Apparatus 102 includes a plurality of inlet conduits inbottom 116 and at least one outlet conduit 120, for example, a “drafttube,” in top 114. Further details of apparatus 102 are illustrated anddescribed with respect to FIG. 5, which illustrates a detailedperspective view of apparatus 102.

As shown in FIG. 4, drying and collecting apparatus 104 is mounted aboveapparatus 102 and is adapted to receive particulate material 118 fed byapparatus 102 through conduit 120. Apparatus 104 also includes a vessel212, for example, a circular cylindrical vessel, having a substantiallyclosed top 214 and a substantially closed bottom 216 and, according toaspects of the invention, contains particulate material 119 transferredfrom apparatus 102, for example, coated particulate material 118.Apparatus 104 includes at least one inlet in communication with the atleast one outlet conduit 120 from apparatus 102 and at least one outletconduit 220 in top 214. Though closed bottom 216 may comprise anyconventional vessel geometry, in the aspect of the invention shown inFIGS. 3 and 4, bottom 216 comprises an eccentric conical bottom, forexample, offset to avoid interference with conduit 120. Bottom 216 mayinclude one or more outlets 218 for discharging treated particulatematerial 119, for example, to storage or further treatment. Outlet 218may be in direct communication with one or more inlets 133 intoapparatus 102, for example, via one or more conduits 222, wherebytreated particulate material 119 may be re-introduced to apparatus 102for further treatment, for example, for further coating. Conduit 222 mayinclude one or more flow control or flow isolation devices.

FIG. 5 is a detailed perspective view of the feeding and treatingapparatus 102 shown in FIGS. 3 and 4 and FIG. 6 is a cross-sectionalview of the detailed perspective view of bottom 116 of apparatus 102shown in FIG. 5. As shown, bottom 116 comprises a conical divergenttransition 117 having divergent side walls, an inlet 128, mounted byflange 132, directed to the apex of conical transition 117, and aplurality of inlets 130 directed into the divergent sidewalls oftransition 117. Conical transition 117 surrounds an open end 122 ofconduit 120, that is, a “draft tube,” and is mounted to vessel 112 bymeans of flange 134. According to aspects of the invention, bottom 116also includes a nozzle 140 having an orificed end 142 adapted to directa fluid stream toward the open end 122 of conduit 120. For example,nozzle 142 may be provided by model F24-SU2A nozzle provided by SprayingSystems Company. Typically, nozzle 140 may be centrally located withininlet 128, for example, mounted by two or more equally-spaced supportspositioned about the inside diameter of inlet 128 and, possibly, alongthe length of inlet 128.

In a manner similar to that described with respect to FIG. 2 above,according to aspects of the invention, as a fluid, for example, a gas ora liquid, is introduced to inlet 128, the fluid enters vessel 112 andentrains at least some particulate material 118 (not shown) into openend 122 of conduit 120 and transfers particulate material 118 throughconduit 120. The entrainment and/or transfer of the particulate material118 may be supplemented or augmented by introducing one or more fluidsvia inlets 130. As noted above, the fluidization of the particulatematerial 118 and the consequent creation of a pressure differentialbetween the open end 122 of conduit 120 and the distal open end 124 ofconduit 120 promotes the flow of the aerated particulate material 118from open end 122, through conduit 120, and out of open end 124 inapparatus 104.

Again, as discussed above, according to aspects of the invention, whilematerial 118 is agitated, aerated, or fluidized by fluid introduced byinlet 128 and/or inlets 130, at least one further fluid is introduced bymeans of nozzle 140 to contact the dispersed material 118 with fluid. Inone aspect, the fluid introduced via nozzle 140 may comprise a fluidhaving a non-volatile component which is adapted to at least partiallycoat the individual particles of material 118. In one aspect, at leastsome of the surface of particulate material 118, for example, at least25% of the surface, is coated with a least some of the non-volatilecomponent of the fluid. In another aspect of the invention, at least 50%or even at least 75%, of the surface area of particulate material 118receives at least some of the non-volatile component of the fluid. Insome aspects more than 90% or even substantially 100% of the surfacearea of material 118 may be covered or coated.

During or after coating material 118 with the fluid, the fluid isallowed to “dry” onto the surface of material 118, for example, byevaporation of any volatile components present in the fluid, whereby atleast one non-volatile component of the fluid adheres to the surface ofparticulate material 118, to provide a coated particular material 119.According to aspects of the invention, this drying or evaporation ofvolatile components may be accelerated by the fluid flow introduced viainlet 128. For example, the fluid introduced via inlet 128 may comprisea fluid having a little or no concentration of the volatile component ofthe fluid introduced to nozzle 140. In another aspect, the fluidintroduced to inlet 128 may be heated, for example, heated air, toenhance evaporation of the volatile components of the fluid introducedthrough nozzle 140. In another aspect of the invention, drying orevaporation may be promoted by heating the vessel 112, for example,heating the bottom 116 and/or the transition 117. The heating of vessel112 may practiced with an internal or external heating device, forexample, a heat exchanger mounted about vessel 112 with appropriateinsulation.

With the aid of the illustrations of the aspects of the invention foundin FIGS. 1 through 6, the following discussion will illustrate andunderscore the advantages of aspects of the present invention comparedto the prior art. The present invention, which may be referred to in theart as a type of draft-tube-spout, fluid-bed (DTSFB) apparatus, providesimprovements over prior art DTSFB apparatus. For example, as discussedabove, according to aspects of the present invention, a DTSFB apparatusis provided in which the feeder section, that is, apparatus 102 in FIGS.3 and 4, is separated from the separator section, that is, apparatus 104in FIGS. 3 and 4. This arrangement allows the fluid flow rate in thedraft tube, for example, tube 120 in FIGS. 3 and 4, and the pressuredrop across the draft tube to be independently specified. As a result,either the solids fraction flowing through the draft tube, the particlevelocity flowing through the draft tube, or both of these parameters canbe set and varied, for example, independently set and varied.

The inventors have established that the particle mass flux through adraft tube, W_(d), can be defined as a function of solids fractionflowing through draft tube, (1−ε_(d)); the particle density, ρ_(p); andthe particle velocity, v_(d), by the relationship in Equation 1.W _(d)=(1−ε_(d))ρ_(p) v _(d)  [Equation 1]According to aspects of the invention, as a result of the relationshipdefined by Equation 1, the processing time of the particles (that is,the transit time of the particles in the draft tube as defined byparticle velocity, v_(d)) and the environment in which the particles areprocessed (that is, the solids fraction of the particles in the drafttube) can both be varied independently. This versatility contrasts withprior art DTSFB apparatus in which only one of these parameters (thatis, particle velocity time or solids fraction) can be specifiedindependently.

This limitation of the prior art is associated with the typicalinability of prior art DTSFB mixers to differentiate the pressure dropacross the draft tube (for example, the dynamic pressure difference fromthe inlet 22 to the outlet 24 of draft tube 20 in FIG. 1) from thepressure drop across the annular bed (for example, the pressuredifference from the bottom of the annular bed 26 from the bottom ofvessel 12 to the void space 21 at the top of the particulate material 18in FIG. 1). For example, a typical prior art DTSFB apparatus isillustrated in FIG. 1 of Plawky, et al. (2003), in which the outlet ofthe draft tube and the top of the DTSFB vessel are in fluidcommunication, that is, are at relatively the same pressure. Incontrast, according to aspects of the present invention, these pressuredrops can be different and varied independently. This advantage ofaspect of the present invention will be elaborated up further below.

The pressure drop across the annulus of a DTSFB apparatus, that is, inboth prior art apparatus and aspects of the present invention, may bedetermined as a function of the flows to the inlet of the DTSFBapparatus. Once these flow rates are defined, the rate of fluid flow,for example, the rate of mass fluid flow, through the draft tube isdetermined by a material balance of the flows into and out of the inletof the DTSFB apparatus, for example, as illustrate by the flows shown inFIG. 2. The material balance about vessel 12 (see FIG. 1) is defined byEquation 2:F _(d) =F _(jo) +F _(axo) +F _(s) −F _(a).  [Equation 2]Where, in Equation 2,

F_(d)=the mass fluid flow rate in the draft tube, arrow 23 in FIG. 2;

F_(jo)=the mass fluid flow rate through the inlet nozzle, arrows 36 inFIG. 2;

F_(axo)=the mass fluid flow rate through the auxiliary nozzles, arrow 37in FIG. 2;

F_(s)=the mass fluid flow rate through the spray nozzle, for example,the coating fluid, arrow 41 in FIG. 2; and

F_(a)=the mass fluid flow rate through the annulus, arrows 42 in FIG. 2.

Again, once the draft tube flow rate, F_(d), and the solids fraction,(1−ε_(d)), are established, the pressure drop across the draft tube,ΔP_(d), may be defined. By varying any one of the flow rates in Equation2, the pressure drop across the draft tube, ΔP_(d), may be varied. Asnoted above, typically, in prior art DTSFB apparatus the pressure dropacross the draft tube must be substantially the same as the pressuredrop across the annular bed. However, according to aspects of thepresent invention, the pressure drop across the draft tube may vary fromthe pressure drop across the annular bed.

According to other aspects of the invention, the fluid velocity and theparticle velocity or their difference in the draft tube are a functionof the drag force on the particles. That is, once the fluid velocity isknown, the particle velocity may also be known. Moreover, in aspects ofthe invention, changes in the particle velocity may be effected byvarying the inlet flow conditions, for example, by varying the massfluid flow rate through the inlet nozzle, F_(jo); varying the mass fluidflow rate through the auxiliary nozzles, F_(axo); and/or varying themass fluid flow rate through the annulus, F_(a). According to aspects ofthe invention, once the particle velocity is fixed or known, the solidsfraction, (1−ε_(d)), can be varied by varying the pressure drop, ΔP_(d),across the draft tube.

Prior art DTSFB apparatus require the determination of the split in massflow between the draft tube, F_(d), and the annulus, F_(a). This data istypically obtained through experimentation on the specific apparatusused. For example, no general guidance or predictions of this flow splitis available in the prior art literature. If F_(a) is fixed or known,F_(d) can be determined; but again, in the prior art, the pressure dropacross the annulus, ΔP_(a), and the pressure drop across the draft tube,ΔP_(d), are typically the same. Aspects of the present invention are notlimited by this restriction; that is, in aspects of the presentinvention, the pressure drop across the annulus, ΔP_(a), and thepressure drop across the draft tube, ΔP_(d), may, and typically will, bedifferent. This distinction can provide enhanced operational versatilityto aspects of the present invention compared to the prior art.

These limitations of prior art DTSFB apparatus are particularly acutewhen handling low-density particulate, such as aerogel beads.Specifically, when attempting to handle low-density particulate materialin prior art DTSFB apparatus, the annulus pressure drop, ΔP_(a), willtypically impose an undesirably high-pressure drop across the drafttube, ΔP_(d). Light, low-density particles typically do not require ahigh-pressure drop across the draft tube to transport the particlesthrough the draft tube. As a result, should the operating regime of theprior art DTSFB apparatus impose a relatively higher pressure dropacross the annulus, ΔP_(a), a comparable relatively higher pressure dropwill also be imposed across the draft tube. Due to the low-density ofthe particles, such a higher pressure drop across the draft tube willpropel a higher solids fraction through the draft tube, which typicallymay be undesirable, especially, in coating applications.

In contrast, according to aspects of the present invention, the pressuredrop across the draft tube, ΔP_(d), and the pressure drop across theannulus, ΔP_(a), may be independent; that is, the pressure drop acrossthe draft tube, ΔP_(d), may not be dictated by the annulus pressuredrop, ΔP_(a). According to aspects of the invention, the pressure dropacross the draft tube may be relatively low, for example, lower than thepressure drop across the annulus. For instance, when transportinglow-density particulate material, for example, aerogel beads (having andensity of about 140 kg/m³) that can be transported with a lowerpressure drop across the draft tube, aspects of the present inventionare far superior to prior art DTSFB apparatus.

Though theoretically, when handling low-density materials, such asaerogel beads, in a prior art DTSFB apparatus, the pressure drop acrossthe draft tube may simply be reduced by lowering the pressure dropacross the annulus, for example, by reducing the bed height in theannulus. However, the inventors have found that, though the pressuredrop across the annulus can be reduced by reducing the bed height of theparticulate material in the annulus, in practice, the desirable pressuredrops across the draft tube for low-density materials require that thepressure drop across the annulus, and the bed height, may be markedlylow. As a result, such low bed heights are difficult, if not impossible,to maintain in practically-designed DTSFB apparatus. Only by usingaspects of the present invention, where the draft tube pressure drop maybe independent of the annulus pressure drop, is the handling oflow-density particulate material, such as, aerogel beads, practical oreven possible. However, aspects of the invention may also be used tohandle high-density particulate material, for example, glass beads.

The aspects of the invention illustrated in FIGS. 3 through 6 were usedby the inventors to coat particulate material according to aspects ofthe invention. Prior to formal experimentation, as is typical, theinventors investigated the desirable sizes and operating parameters. Thefollowing investigation, experimentation, aspects of the invention arediscussed with reference to the use of aerogel beads as the particulatematerial. However, the inventors recognize and it is to be understoodthat aspects of the invention may be applied to any particulatematerial, including but not limited to pharmaceuticals; food stuffs;cosmetics; metals, such as, powder manufacturing powder metals;ceramics; and like particulates.

The inventors' objective in performing the following investigation wasto produce a coated aerogel bead and/or a coated aerogel bead material,for instance, a material that can be applied to a surface, for example,by spraying, or formed into a desired shape, for example, by molding. Inone aspect, the coated aerogel bead and/or material may comprise aninsulating material, for example, a thermal or electrical insulatingmaterial. In the following experiments, the aerogel beads used comprised1 to 3 mm aerogel beads provided by Cabot Inc., though any similar orequivalent aerogel beads may be used in aspects of the invention.

According to one aspect and as described below, a method may bepracticed using a DTSFB apparatus as described in FIGS. 1-6; however,the inventors recognize that aspects of the invention may also bepracticed in other apparatus that are adapted to perform the methodsrecited. The DTSFB apparatus may be adapted to agitate and/or suspendthe aerogel beads in a first fluid, for example, air, nitrogen, or aninert gas, among other gases, and then exposing the agitated and/orsuspended aerogel to a second fluid, that is, the “coating fluid,”containing at least one volatile component and at least one non-volatilecomponent whereby when the volatile component are allowed to volatilizeor evaporate at least some of the non-volatile component remains on thesurface of the aerogel beads. In this discussion and in the descriptionof aspects of the invention that and in the attached claims, a“non-volatile” component comprises a component of the liquid that is notvolatile under the temperature and pressure conditions under which theprocess is performed, for example, at a temperature less than about 250degrees C. (about 482 degrees F.) and a pressure less than 2atmospheres. Conversely, a “volatile component” is one that doesvolatilize or evaporate under the temperature and pressure conditionsunder which the process is performed. For example, in the investigationdescribed below, the second fluid comprises a fluid containing anon-volatile polymer and a volatile component, such as, water, alcohol,or a solvent, that is introduced to the beads as a spray or fine mist.According to one aspect of the invention, attrition, wear, or damage tothe aerogel beads is minimized or prevented. In addition, according toone aspect of the invention, the volatile component of the second fluidvolatilizes or evaporates quickly enough that substantially little or nopenetration of the aerogel bead by the second fluid occurs.

In order to better understand the potential for penetration of thesecond fluids in to the aerogel beads, the inventors proposed thefollowing relationships in Equations 3 and 4.

$\begin{matrix}{{\frac{\Delta\; P}{\Delta\; x} = \frac{P_{atm} - \left( {\gamma/r_{0}} \right)}{L_{pore}}}{and}} & \left\lbrack {{Equation}\mspace{20mu} 3} \right\rbrack \\{v_{avg} = {{- \left( {{\_\Delta}\;{P/\Delta}\; x} \right)}{r_{o}^{2}/\left( {8µ} \right)}}} & \left\lbrack {{Equation}\mspace{20mu} 4} \right\rbrack\end{matrix}$where

ΔP/Δx is the driving pressure drop radially into the pores of theaerogel bead, N/m³;

P_(atm) is the prevailing atmospheric pressure, assumed 101,000 N/m²;

γ is the surface tension of the second fluid, assumed 26.9×10⁻³ J/m²;

r_(o) is the radius of the aerogel beads, assumed 10 nanometers [nm];

L_(pore) is the length the pore in the surface of the bead, assumed 1micrometer [μm];

v_(avg) is the average velocity of the second fluid through the pores ofthe aerogel beads, mm/s; and

μ is the viscosity of the second fluid, assumed 1 N−s/m².

By evaluating Equations 3 and 4 with the assumed values, the followingparameters were estimated for the processing of aerogel beads.

$\frac{\Delta\; P}{\Delta\; x} = {{- 2.7} \times 10^{11}\mspace{11mu} N\text{/}m^{3}}$and v_(avg) = 3.3 × 10⁻³  mm/s.The resulting design specifications for the experiments performed arelisted in Table 1 and the resulting design calculation parameters appearin Table 2.

TABLE 1 DTSFB Apparatus Aerogel Coating Design Specifications Fluid,particle, Particle Density (ρ_(g)) 140 kg/m³ and bed Air Density(ρ_(f)), at 298 K 1.165 kg/m³ properties Air Viscosity (μ_(f)) at 298 K18.64 × 10⁻⁶ Ns/m² Annulus Voidage (ε_(a)) 0.42 Geometric Particlediameter (d_(p)) 1 mm Properties Draft tube diameter (D_(d)) 41.15 mmDraft tube length (l_(d)) 2 m Annulus inner diameter (D_(i)) 44.45 mmAnnulus Outer diameter (D_(o)) 149.1 mm Height of particles in annulus(H_(a)) 0.5 m Inlet flow rates Jet and Auxiliary flow (F_(jo) + F_(axo))866 liters/min. Spray flow (F_(s)) 34 liters/min. Total flow 900liters/min. Draft tube Superficial air velocity (U_(d)) 10 m/sconditions Solids fraction (1 − ε_(d)) 0.01

TABLE 2 DTSFB Apparatus Aerogel Coating Design Calculation Results Drafttube pressure drop (ΔP_(d)) 96.2 Pa (0.386 in. of H₂O) Annulus pressuredrop (ΔP_(a)) 236.6 Pa (1.07 in. of H₂O) Particle flux (W_(d)) 12.6kg/m²s Particle Mass Flow (G_(d)) 0.0167 kg/s Minimum FluidizingVelocity (U_(mf)) 0.043 m/s Slip Velocity (U_(a) + v_(a)) 0.042 m/sTerminal Velocity (U_(T)) 1.133 m/s Superficial air velocity (U_(d)) 10m/s

According to aspects of the invention, apparatus 100 shown in FIGS. 3through 6, was operated under the conditions listed in Tables 1 and 2.In addition the spray nozzle 140 shown in FIG. 6 was operated under theconditions that appear in Table 3. In these experiments, spray nozzle140 comprised a SU2A atomizing spray nozzle system provided by SprayingSystems Company, though in aspects of the invention any similar orequivalent commercially available spraying system may be used.

TABLE 3 DTSFB Apparatus Aerogel Coating Spray Nozzle Parameters Nozzleorifice diameter 0.020 inches Air Pressure 4-60 psig Air Capacity0.8-2.7 scfm Liquid pressure 3-40 psi Liquid capacity 2-284 ml/min.Spray time <10 mins.

The aerogel beads were provided to vessel 112 in system 102 from a beadsource (not shown) by means of a bead hopper (not shown) having apneumatic injector, though other types of transfer systems may be used.The transport fluid in system 102, that is, the fluid introduced toinlets 144 and 130 (that is, F_(jo)+F_(axo)), comprised ambient airheated to about 50 degrees C. and introduced at the rate that appears inTable 1. The transport fluid may range in temperature from about 10degrees C. to about 150 degrees C., for example, from 30 degrees C. toabout 100 degrees C. In one aspect, vessel 112 may also be heated, forexample, by means of a thermal blanket or by means of a heat exchangerthrough which a heated fluid, for example, air or water, may be passed.The walls of vessel 112 may be heated to about 10 degrees C. to about150 degrees C., for example, from 30 degrees C. to about 100 degrees C.In these experiments, the walls of vessel 12 were heated to about 40degrees C.

The coating fluid in system 102, that is, the fluid introduced to inlets140 (that is, F_(s)) comprised one of fluids listed in Table 4. Thecoating fluid may be heated, for example, to a temperature ranging fromabout 10 degrees C. to about 250 degrees C., for example, from 30degrees C. to about 100 degrees C.

TABLE 4 DTSFB Apparatus Aerogel Coating Fluids Colorcon OPADRY IIpolyvinyl alcohol, water-based cationic polymer Eudragit¹ L30 D55polymethyl methacrylate, water-based anionic polymer Eudragit¹ E12,5polymethyl methacrylate, solvent-based cationic polymer Eudragit¹ NE30 Dpolymethyl methacrylate, solvent-based neutral polymer Eudragit¹ RL 12,5polymethyl methacrylate, solvent-based cationic polymer Water-bornepolyurethane solution ¹Eudragit solutions can be mixed with virtuallyany solvent to control viscosity, surface tension, etc., as needed.

During processing, the aerogel beads in vessel 112 are agitated,aerated, and transported into the open end 122 of conduit 120. Atsubstantially the same time as this agitation and transport, a coatingfluid is introduced by means of spray nozzle 140 to the vicinity of theopen end 122 whereby at least some of the aerogel beads are exposed tothe coating fluid. The coated beads are then transported throughconduit, or draft tube, 120 to vessel 212 in apparatus 104 anddischarged from open end 124 of conduit 120. According to the aspects ofthe present invention, the at least partially coated aerogel beads thatare discharged from open end 124 may typically settle to the bottom ofvessel 212, for example, in the off-set conical bottom of vessel 212. Inone aspect, the at least partially coated beads may then be forwarded tofurther processing, or returned to apparatus 102 for further coating,for example, via conduit 222 and inlet 133 in top 114 of vessel 112. Forexample, in one aspect, the aerogel beads may be treated, that is,coated, in apparatus 102 repeatedly, for example, at least twice, butmay be recycled from apparatus 104 to apparatus 102 three or more, orfour or more times, depending upon, among other things, the size of theparticles being coated and the amount or extent of coating desired.

While the coated aerogel beads may be recirculated to apparatus 102, thefluid stream introduced to vessel 212 via conduit 120 may be dischargedfrom vessel 212, for example, from one or more outlets 220, andforwarded to re-use as a transfer medium or for further processing. Forexample, the fluid, typically, gaseous, stream discharged from vessel212 may be treated to remove any aerogel beads or other particulate. Forinstance, the fluid stream discharged from vessel 212 may be scrubbed orfiltered, for example, filtered in a conventional “bag-house” filter orother filtering medium (not shown), prior to being further processed orre-used.

FIGS. 7 through 10 illustrate typical coated aerogel beads produced withthe apparatus 100 shown in FIGS. 3 through 6 according to one aspect ofthe invention. FIG. 7 illustrates a magnified view of aerogel beadscoated in a first trial according to aspects of the invention asmagnified 20 times. FIG. 8 illustrates a magnified view of one coatedaerogel bead produced in the same trial as the beads shown in FIG. 7when magnified 50 times. In this first trial, the aerogel beads werecoated with a pharmaceutical grade polyvinyl alcohol, specifically,Opradry II polyvinyl alcohol. The beads were coated for a totalprocessing time of about 1 minute at a temperature of about 90 degreesC. The results of this trial produced coated beads with substantially nopenetration of the coating fluid into the beads and minimal beadattrition due to processing.

FIG. 9 illustrates a magnified view of aerogel beads coated in a secondtrial according to aspects of the invention as magnified 20 times. FIG.10 illustrates a magnified view of coated aerogel beads produced fromthe same second trial as FIG. 9 when magnified 50 times. In this secondtrial, the aerogel beads were again coated with a pharmaceutical gradepolyvinyl alcohol, specifically, Surelease brand polyvinyl alcohol. Thebeads were coated for a total processing time of about 10-20 minutes ata temperature of about 90 degrees C. The results of this second trialproduced coated beads with substantially no penetration of the coatingfluid into the beads, minimal bead attrition due to processing, and morecompete, smoother coverage of the bead surface than produced from thefirst trial. Some difficulties with the spraying nozzle were encounteredin the second trial, which may have impacted the uniformity of theparticle coating. The inventors believe that improved control of thetemperature of the sprayed coating will likely overcome this difficulty.

Examination of the coated aerogel particles shown in the photographs ofFIGS. 8 and 10 clearly illustrate the presence of coating material onthe surface of the aerogel particles. Though these photographsillustrate the partial coating of the surface of the aerogel particles,even this particle coating provides particles having enhancedproperties. However, according to aspects of the invention, the extentof the coverage or coating of aerogel particles can be enhanced by,among other things, repeated exposure to the coating fluid, for example,by recycling of the particles for repeat treatment in apparatus 100, oroptimization of the operating parameters of the treatment, for example,varying the temperature or rate of flow of the coating fluid. These andother modifications of aspects of the present invention are includedwithin the scope of aspects of the invention.

In any event, the first and second coating trials with apparatus 100illustrated in FIGS. 3 through 6, clearly illustrate the effectivenessof aspects of the present invention when coating aerogel beads toproduce an aerogel-based material, for example, an insulation material.The coated beads exhibit little or no penetration of the coating fluidinto the beads while subjecting the beads to little or no wear orattrition, thus ensuring the integrity of the beads, especially, theirinsulating properties. The inventors are optimistic that apparatus 100can be an effective device for coating other types of particulatematerial, for example, other types of low-density particulate material,that can, for example, provide the designer a novel material for anyapplication where thermal or electrical insulation is desired.

While several aspects of the present invention have been described anddepicted herein, alternative aspects may be provided by those skilled inthe art to accomplish the same objectives. Accordingly, it is intendedby the appended claims to cover all such alternative aspects as fallwithin the true spirit and scope of the invention.

1. A particulate material coating apparatus comprising: a vessel havinga top and a bottom, the vessel adapted to contain the particulatematerial; a vertically extending conduit having an inlet in the vesseland an outlet outside of the vessel; a first fluid inlet in the bottomof the vessel, the first fluid inlet directed toward the inlet of thevertically extending conduit wherein a flow of a first fluid introducedby the first fluid inlet produces a flow of at least some of theparticulate material and the first fluid through the verticallyextending conduit; a second fluid inlet in the bottom of the vessel, thesecond fluid inlet adapted to introduce a second fluid to the flow offluid introduced by the first fluid inlet, the second fluid adapted toadhere to the surface of at least some of the particulate material; anda fluid outlet from the vessel.
 2. The apparatus as recited in claim 1,wherein the second fluid inlet is adapted to introduce the second fluidin the form of spray.
 3. The apparatus as recited in claim 1, whereinthe second fluid inlet comprises an orifice.
 4. The apparatus as recitedin claim 3, wherein the orifice comprises an inside diameter of about0.020 inches.
 5. The apparatus as recited in claim 1, wherein the secondfluid inlet is positioned within the first fluid inlet.
 6. The apparatusas recited in claim 5, wherein the second fluid inlet is positionedconcentric with the first fluid inlet.
 7. The apparatus as recited inclaim 1, further comprising means for regulating the flow of fluid fromthe fluid outlet from the vessel wherein at least one parameter of theflow of the particulate material and fluid though the verticallyextending conduit is varied.
 8. The apparatus as recited in claim 1,wherein the apparatus further comprises at least one third fluid inletpositioned in the bottom of the vessel.
 9. The apparatus as recited inclaim 8, wherein the at least one third fluid inlet is adapted tointroduce the first fluid.
 10. The apparatus as recited in claim 1,wherein the bottom of the vessel comprises a conical head having an apexand converging sides, and wherein the first fluid inlet is positioned atthe apex of the conical head.
 11. The apparatus as recited in claim 1,wherein the vessel comprises an inverted frusto-conical top sectionhaving a substantially closed top and an open bottom, a circularcylindrical section having an open top mounted to the open bottom of thefrusto-conical top section, and an inverted frusto-conical bottomsection having an open top mounted to the circular cylindrical sectionand a substantially closed bottom.
 12. The apparatus as recited in claim1, wherein the fluid outlet from the vessel is positioned in the top ofthe vessel.
 13. The apparatus as recited in claim 1, wherein the vesselcomprises a first vessel, and wherein the apparatus further comprises asecond vessel positioned to receive the flow of particulate material andfluid from the vertically extending conduit, the second vessel having atop and a bottom.
 14. The apparatus as recited in claim 13, wherein theapparatus further comprises a conduit for transferring particulatematerial from the second vessel to the first vessel.
 15. The apparatusas recited in claim 13, wherein at least some fine particulate materialis produced in the second vessel, and wherein the device furthercomprises means for collecting at least some of the fine particulatematerial.
 16. The apparatus as recited in claim 15, wherein the meansfor collecting at least some of the fine particulate material comprisesa filtering medium.
 17. The apparatus as recited in claim 16, whereinthe filtering medium comprises at least one bag filter positioned in thesecond vessel.
 18. The apparatus as recited in claim 7, wherein the atleast one parameter of the flow of the particulate material and fluidthough the vertically extending conduit comprises at least one ofparticle velocity, fluid velocity, and voidage.
 19. The apparatus asrecited in claim 1, wherein the particulate material comprises aerogelbeads.
 20. The apparatus as recited in claim 19, wherein the apparatusis adapted to seal at least some pores in the aerogel beads.
 21. Theapparatus as recited in claim 1, wherein the second fluid comprises atleast one non-volatile material adapted to adhere to the surface of atleast some of the particulate material.
 22. The apparatus as recited inclaim 1, wherein the second fluid comprises at least one volatile fluidand at least one non-volatile material adapted to adhere to the surfaceof at least some of the particulate material.
 23. The apparatus asrecited in claim 1, wherein the second fluid comprises at least one ofan alcohol, a water-based polymer, a solvent-based polymer, and apolyurethane.
 24. The apparatus as recited in claim 1, wherein the firstfluid comprises air.